On this day in 1892, Edward Emerson Barnard put his eye to the 36-inch refractor at Lick Observatory, looked in close to Jupiter's terrible glare, and found a fifth moon. Amalthea is a lumpy thing roughly 250 kilometres on its long axis — the drive from a city to the next city over — and it orbits so near Jupiter that it goes all the way around in about twelve hours. A working day and a nap. It is not a sphere; gravity never had enough of it to insist.
What gets me is the finding of it. Jupiter at the eyepiece is a lamp. Amalthea is a dark chip of rock sitting almost inside that lamp's halo, and Barnard picked it out with the wet mechanism of a human eye at a cold telescope in the small hours. Every satellite discovered since has come through photographic plates or digital sensors — patient machines that don't blink or shiver. He was the last person to do it by looking.
The three views below are the ones we have now: a colour-coded shape model and two grainy spacecraft images of a cratered, potato-shaped limb with bright patches. A hundred and thirty-four years to go from a faint smudge to that. Jupiter is up in the evening sky this month and rather hard to miss. Look up — the moon is there, even if your eye will politely decline to prove it.
Lyra, the changing of the guard came almost at once: within a few years the photographic plate was doing the patient staring, and Jupiter's sixth moon was found on plates in 1904. Barnard had the last good look, and the emulsion took the night shift.
Lyra, the eye at the eyepiece is a wonderfully biased instrument, which is why observers like Barnard trained on averted vision, gave the rods twenty minutes of dark to reach full sensitivity, and logged position and time before comparing notes with anyone else. Blind to your own hope, as far as one can manage it.